(a) Field of the Invention
The invention relates to a novel tetracarboxylic dianhydride and its derivatives and production. Particularly, it relates to a tetracarboxylic dianhydride useful for producing polyimide precursors or polyimides having low thermal expansion and low residual stress and being suitable for preparing photosensitive resin compositions, and relates to the production and derivatives thereof. The polyimide precursors afford the photosensitive resin compositions with good i-line transmissivity, high-speed developability, high resolution and good dimensional accuracy to suit them to the production of interlayer insulating films or surface-protecting films in semiconductor devices.
It also relates to a polyimide precursor and a polyimide with good heat resistance and good i-line transparency, to a resin composition which contains them and is useful for electronic parts such as semiconductor devices or multilayer wiring boards, and to electronic parts.
It also relates to a photosensitive resin composition and its use for forming relief patterns, and to electronic parts. It particularly relates to a negative or positive, photosensitive resin composition, its use for forming relief patterns and electronic parts using it, which has good i-line transmissivity and, on heating, is capable of being into a heat-resistant polyimide polymer suitable for surface-protecting films, interlayer insulating films and others for electronic parts such as semiconductor devices.
(b) Description of the Related Art
A recent tendency in semiconductor industries has been to replace conventional inorganic interlayer insulating materials with highly heat-resistant organic materials such as polyimide resins because of the characteristic advantages that such organic materials offer.
Circuit patterning on semiconductor integrated circuits or printed boards needs various complicated steps, including coating substrate surfaces with resists, exposing predetermined areas, removing unnecessary parts by etching or the like and washing the substrate surfaces. This has raised a desire to new heat-resistant photosensitive materials which can remain as insulating materials on desired areas after formed into patterned resists by exposure and development.
For example, there have been proposed heat-resistant photosensitive materials containing photosensitive polyimides or cyclized polybutadienes as base polymers, and photosensitive polyimides are particularly noted for their good heat-resistance and easy removal of impurities.
The first-proposed photosensitive polyimides comprise a polyimide precursor and a dichromate (Japanese Patent Application Examined Publication No. 49-17374). In spite of their practical photosensitivity and good film formability, they have found no practical use due to poor storage stability and the residual chromium ion in the product polyimides.
It has been proposed to evade these drawbacks by, for example, mixing polyimide precursors with compounds having photosensitive groups (Japanese Patent Application Unexamined Publication No. 54-109828), or by introducing photosensitive groups into polyimide precursors through the reaction of the functional groups of the polyimide precursors with the functional groups of compounds having the photosensitive groups (Japanese Patent Application Unexamined Publication Nos. 56-24343 and 60-100143).
Such photosensitive polyimide precursors, however, suffer from low sensitivity and defective patterns. This is attributable to the main skeleton derived from aromatic monomers, which contributes good heat-resistance and excellent mechanical properties but makes the polyimide precursors themselves absorb light, thereby lowering the transparency to ultraviolet light and hindering effective photochemical reactions in the exposed areas.
In addition, today""s high integration on semiconductors requires increasing preciseness in fabrication rule and higher resolution.
To meet these needs, the conventional contact/proximity aligners using parallel light are being replaced by 1:1 projection aligners called mirror projectors, and further by reduction projection aligners called steppers.
Steppers use a monochromatic light, such as a high-power frequency light of ultra-high-pressure mercury-vapor lamps or an excimer laser. Most of the conventional steppers are g-line steppers using a visible light (435 nm wavelength) of ultra-high-pressure mercury vapor lamps, which is called g-line. The increasing preciseness of fabrication rule, however, needs steppers using light of shorter wavelengths, and i-line steppers (wavelength: 365 nm) are taking the place of g-line steppers (wavelength: 435 nm).
Nevertheless, for the above-mentioned reasons, conventional photosensitive polyimide-based polymers designed for contact/proximity aligners, mirror projection aligners and g-line steppers have poor transparency, particularly almost no transparency to 1-line (wavelength: 365 nm), and cannot form desired patterns with 1-line steppers.
LOC (Lead On Chip system), which is a high-density semiconductor packaging system, needs thicker surface-protecting polyimide films. The thicker the films, the deeper the problem of poor transparency. Therefore, there is a strong desire for photosensitive polyimides which have a high i-line percent transmittance and form polyimide patterns of good profile by exposure with i-line steppers.
On the other hand, as the diameter of silicon wafers to be substrates has increased with the years, there has arisen the problem of larger warp of silicon wafers coated with surface-protecting polyimide films due to the difference between polyimides and silicon wafers in thermal expansion coefficient. This raised another strong desire for photosensitive polyimides which are much less thermally expansive than conventional polyimides. Rigidly structured molecules generally contribute to decreasing the thermal expansion, but aggravate photosensitivity due to their little transparency to i-line. Flexibly structured molecules decrease the stress applied to silicon wafers to decrease warp and can transmit i-line, but cannot afford the good heat-resistance required of polyimide surface-protecting films.
To improve the i-line transmissivity, it has been proposed to introduce fluorine into polyimides (Japanese Patent Application Unexamined Publication No. 8-234433) or to bend the molecule chains of polyimides (Japanese Patent Application Unexamined Publication No. 8-36264). Nevertheless, fluorine-containing polyimides are less adhesive to silicon wafers, and aggravate the reliability of semiconductor elements. The polyimides having bent molecule chains have poor heat-resistance and high thermal expansion coefficient due to the weak mutual interaction of molecules, and aggravate the reliability of semiconductor elements.
An object of this invention is to provide a novel tetracarboxylic dianhydride, a novel tetracarboxylic acid, its derivatives and a method of producing it. They are useful as raw materials for polyimide precursors which have not only a rigid structure ensuring low thermal expansion and good heat-resistance but also an i-line transmissivity enough for practical applications.
This invention provides a 6,6xe2x80x2-dialkyl-3,3xe2x80x2,4,4xe2x80x2-biphenyltetracarboxylic dianhydride represented by general formula (1): 
wherein R1 and R2 each independently represent an alkyl group.
In one embodiment of the invention, the R1 and R2 in the general formula (1) are methyl groups.
This invention further provides a 6,6xe2x80x2-dialkyl-3,3xe2x80x2,4,4xe2x80x2-biphenyltetracarboxylic acid or a derivative thereof, which is represented by general formula (2): 
wherein R1 and R2 each independently are an alkyl group, R3, R4, R5 and R6 each independently are a hydrogen atom, an alkyl group, an alkali metal ion or an ammonium ion.
This invention further provides a method of preparing a 6,6xe2x80x2-dialkyl-3,3xe2x80x2,4,4xe2x80x2-biphenyltetracarboxylic dianhydride, comprising brominating a 4-alkylphthalic anhydride at its 5-position, and then coupling the bromination product in the presence of a nickel catalyst.
In one embodiment of the invention, the method comprises heating a water suspension of a 4-alkylphthalic anhydride and a bromate and adding thereto concentrated sulfuric acid to form a 4-alkyl-5-bromophthalic acid, esterifying the 4-alkyl-5-bromophthalic acid to form a 4-alkyl-5-bromophthalic diester, coupling the 4-alkyl-5-bromophthalic diester in the presence of a nickel catalyst to form a 6,6xe2x80x2-dialkyl-3,3xe2x80x2,4,4xe2x80x2-biphenyltetracarboxylic tetraester, hydrolyzing the 6,6xe2x80x2-dialkyl-3,3xe2x80x2,4,4xe2x80x2-biphenyltetracarboxylic tetraester to form a 6,6xe2x80x2-dialkyl-3,3xe2x80x2,4,4xe2x80x2-biphenyltetracarboxylic acid, and dehydrating the 6,6xe2x80x2-dialkyl-3,3xe2x80x2,4,4xe2x80x2-biphenyltetracarboxylic acid into a 6,6xe2x80x2-dialkyl-3,3xe2x80x2,4,4xe2x80x2-biphenyltetracarboxylic dianhydride.
Another object of this invention is to provide a polyimide precursor which has good 1-line transmissivity in spite of their rigid structures and, after imidation, exhibits good heat-resistance. The invention also provides a polyimide derived from the polyimide precursor.
That is, this invention provides a polyimide precursor having repetitive units represented by general formula (7): 
wherein Y is a divalent organic group, R7 and R8 each independently are OH or a monovalent organic group, R9 and R10 each independently are a monovalent hydrocarbon group, R11, R12 and R13 each independently are a monovalent hydrocarbon group, a and b each independently are an integer of 0 to 2, c is an integer of 0 to 4, and m is an integer of 0 to 3.
Herein, every repetitive unit of the polyimide precursor may have any one of three structures including the structure of formula (7), which are structurally isomeric with one another. The two structures other than that of the general formula (7) are represented by the following general formulae (7xe2x80x2) and (7xe2x80x3): 
In one embodiment of the invention, the polyimide precursor has repetitive units represented by general formula (8): 
wherein Y is a divalent organic group, R14, R15, R16, R17 and R18 each independently are a hydrogen atom or an alkyl group, x is 0 or 1, n and p each independently are an integer of 1 to 10.
In one embodiment of the invention, the polyimide precursor has repetitive units of general formula (8) wherein R14, R15, R16 and R18 are hydrogen atoms, and x is 0.
In one embodiment of the invention, n and p in general formula (8) are 1.
Another object of the invention is to provide a polyimide precursor suitable for photosensitive resin compositions.
That is, in one embodiment of the invention, the polyimide precursor has repetitive units of general formula (9): 
wherein Y, R7, R8, R9, R10, R13 and m are as defined above.
In one embodiment, the divalent organic group represented by Y in the general formula (9) is represented by general formula (10): 
wherein R19, R20, R21 and R22 each independently are a hydrogen atom, an alkyl group, a fluorine atom or a fluoroalkyl group, with the proviso that two or more of them are alkyl groups, fluorine atoms or fluoroalkyl groups.
To be suited for negative, photosensitive resin compositions, the polyimide precursor preferably has repetitive units of the general formula (9) wherein at least one of R7 and R8 is a monovalent organic group having a carbonxe2x80x94carbon unsaturated double bond.
To be suited for positive, photosensitive resin compositions, the polyimide precursor preferably has repetitive units of the general formula (9) wherein Y is a divalent organic group having a carboxyl group or a phenolic hydroxyl group. Still preferably, in general formula (9), R7 and R8 are hydroxyl groups.
Another object of this invention is to provide a polyimide which has good i-line transmissivity in spite of its rigid structure and exhibits excellent heat-resistance.
That is, this invention provides a polyimide having repetitive units represented by general formula (11): 
wherein Y is a divalent organic group, R9 and R10 each independently are a monovalent hydrocarbon group, R11, R12 and R13 each independently are a monovalent hydrocarbon group, a and b each independently are an integer of 0 to 2, c is an integer of 0 to 4, and m is an integer of 0 to 3.
In one embodiment of the invention, the polyimide has repetitive units represented by general formula (12): 
wherein Y is a divalent organic group, R16, R17 and R18 each independently are a hydrogen atom or an alkyl group, x is 0 or 1, n and p each independently are an integer of 1 to 10; and in cases R16, R17 and R18 are alkyl groups, one or a plurality of each of R16, R17 and R18 may be bonded to the benzene rings on any positions.
In one embodiment of the invention, the polyimide has repetitive units represented by the general formula (12) wherein R16 and R18 are hydrogen atoms, and x is 0.
In one embodiment of the invention, n and p in the general formula (12) are 1.
Another object of this invention is to provide a resin composition which contains a polyimide or its precursor having good i-line transparency in spite of its rigid structure, and, after imidation, exhibits excellent heat-resistance. It is suitable for forming surface-protecting films or interlayer insulating films in semiconductor devices, or interlayer insulating films in multilayer wiring boards.
That is, the invention provides a resin composition containing the polyimide precursor having repetitive units of the general formula (7) or the polyimide having repetitive units of the general formula (11).
In one embodiment of the invention, the resin composition contains the polyimide precursor having the repetitive units represented by the general formula (8): 
wherein Y is a divalent organic group, R14, R15, R16, R17 and R18 each independently are a hydrogen atom or an alkyl group,
x is 0 or 1, and n and p each independently are an integer of 1 to 10;
or the polyimide having the repetitive units represented by the general formula (12): 
wherein Y is a divalent organic group, R16, R17 and R18 each independently are a hydrogen atom or an alkyl group, x is 0 or 1, and n and p each independently are an integer of 1 to 10.
Another object of the invention is to provide an extremely reliable electronic part, which has a surface-protecting or interlayer insulating film formed from a material having good i-line transmissivity in spite of its rigid structure and exhibiting good heat-resistance after imidation.
That is, the invention provides an electronic part (hereinafter, it may be called xe2x80x9celectronic part (a)xe2x80x9d sometimes) which has a film of the polyimide having the repetitive units of the general formula (11), preferably the general formula (12).
Another object of the invention is to provide a photosensitive resin composition having good i-line transmissivity and high resolution.
That is, the invention provides a photosensitive resin composition which contains the polyimide precursor having the repetitive units represented by the general formula (7).
In one embodiment of the invention, the photosensitive resin composition contains a polyimide precursor having repetitive units represented by general formula (9): 
wherein Y, R7, R8, R9, R10, R13 and m are as defined above.
In one embodiment of the invention, the photosensitive resin composition contains a polyimide precursor having repetitive units of the general formula (9) wherein the divalent organic group Y is represented by general formula (10): 
wherein R19, R20, R21 and R22 are as defined above.
Another object of the invention is to provide a photosensitive resin composition which has the above-mentioned good properties and is suited to negative patterning.
That is, in one embodiment of the invention, the photosensitive resin composition has repetitive units of the general formula (9) wherein at least one of R7 and R8 is a monovalent organic group having a carbonxe2x80x94carbon unsaturated double bond.
Preferably, the photosensitive resin composition further contains a photopolymerization initiator.
Another object of the invention is to provide a photosensitive resin composition which has the above-mentioned good properties and is suited to positive patterning using an aqueous alkali solution for development.
That is, in another embodiment of the invention, the photosensitive resin composition has repetitive units of the general formula (9) wherein Y is a divalent organic group having a carboxyl group or a phenolic hydroxyl group or wherein R7 and R8 are hydroxyl groups, and further contains a compound capable of generating an acid when exposed to light.
In one embodiment of the invention, the compound capable of generating an acid when exposed to light is an o-quinonediazide compound.
Another object of the invention is to provide a method of forming relief patterns with high resolution by exposure using i-line.
That is, the present invention provides a method of forming a relief pattern, comprising a step of applying the photosensitive resin composition of the invention onto a substrate and drying it thereon, a step of exposing it, a step of developing it, and a step of heating it.
In one embodiment of the invention, the exposure is conducted by using i-line as a light for the exposure.
Another object of the invention is to provide an extremely reliable electronic part which has a surface-protecting or interlayer insulating film having a relief pattern of high resolution.
That is, the invention provides an electronic part (hereinafter, it may be called xe2x80x9celectronic part (b)xe2x80x9d sometimes) containing a layer of the relief pattern formed by the method mentioned above.
In one embodiment of the invention, the layer of the relief pattern is a surface-protecting film or a interlayer insulating film.